In ink-jet printing methods, droplets of ink are directly projected onto a recording medium from very fine nozzles and allowed to adhere to the recording medium, to form images or characters. The ink-jet printing methods have become rapidly spread because of various advantages such as easiness of full coloration, low cost, capability of using a plain paper as the recording medium, non-contact with printed images or characters, etc.
In recent years, in order to impart a good weathering resistance and a good water resistance to printed matters, an ink containing a pigment as a colorant component has been extensively used.
On the other hand, there is an increasing demand for commercial printed matters printed on recording media using a low-liquid absorbing coated paper such as an offset-coated paper, or a non-liquid absorbing resin film such as a polyvinyl chloride resin film, a polypropylene resin film and a polyester resin film.
It is known that when images or characters are printed on the low-liquid absorbing or non-liquid absorbing recording media by the ink-jet printing methods, there tends to occur problems such as slow absorption of liquid components, prolonged drying time owing to poor absorption, and deterioration in rub fastness early after printing. Also, it is known that unlike a plain paper in which a pigment is likely to be penetrated, the low-liquid absorbing or non-liquid absorbing recording media tend to suffer from deposition of pigment particles remaining thereon which are directly susceptible to an external force, so that the images or characters printed on these recording media tend to be deteriorated in rub fastness even after being dried.
In order to solve these conventional problems, ink-jet printing methods using recording media having an ink-absorbing layer have been proposed.
For example, JP 2008-260279A discloses an ink-jet printing method using a recording medium having a pigment-containing coating layer in which an amount of pure water transferred to a surface of the recording medium on which the coating layer is provided, and a pH value of the same surface of the recording medium are controlled to respective specific ranges, and images or characters are printed on such a suface of the recording medium using an ink containing a granular coloring material, an emulsion resin and a surfactant and having a pH value of 8 or more. In addition, JP 2008-260279A proposes a recording apparatus equipped with a drying device.
However, the improvement in recording medium and recording apparatus tends to have problems concerning costs, consumed powder, etc., and therefore it is desirable to improve the composition of inks.
JP 2007-138129A discloses a process for producing an aqueous pigment ink composition in which a coloring pigment is dispersed in a mixed solution containing a pigment dispersant and/or a non-water-soluble resin, and a solvent to produce a non-aqueous pigment dispersion, and then the obtained non-aqueous pigment dispersion is mixed with the above non-water-soluble resin to produce a non-aqueous pigment ink, and thereafter an emulsifier and water are added to the thus obtained ink to emulsify and disperse the ink therein. In JP 2007-138129A, it is described that the resulting aqueous pigment ink composition is excellent in storage stability, adhesion and water resistance of printed images or characters, etc.
JP 2005-154549A discloses an aqueous ink composition constituted of a coloring material dispersion including a colorant-containing water-insoluble dispersed resin, acetylene glycol or an ether derivative thereof, a C1 to C5 monovalent alcohol compound and a humectant in which combination of the above alcohol, humectant, acetylene glycol, etc., is selected such that they can be dissolved in each other, and an ink-jet printing method using the aqueous ink composition. In JP 2005-154549A, it is described that the ink composition can satisfy both storage stability and ejection stability.